JPS58125971A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To stabilize the black level, by locating the buried layers in separating each other which are formed at the lower part of each photoelectric converting element group and vertical element group, and at the same time forming a light shielding means at the upper part of an intermediate region. CONSTITUTION:A buried layer 50 of conduction type opposite to a substrate 10 is formed within the substrate 10 provided at the lower part of an area between a diffusion layer 40 forming a light-shielded photoelectric converting element and a vertical register region contiguous with the layer 40. At the same time, a buried layer 51 of conduction type opposite to the substrate 10 is formed within the substrate provided at the lower part of an area between a photoelectric element group 11 and a vertical register group 53 contiguous with the element 11. These layers 50 and 51 are separated from each other, and a high-density region 42 of conduction type same as the substrate 10 is provided between the layers 50 and 51. In such a constitution, the incident light containing near ultraviolet rays is absorbed by a depeletion layer of pn junction formed with the inside of the buried layer of the layer 51, the layer 51 and the substrate 10 and converted into the electric charge. As a result, a factor which induces the fluctuation of black level is deleted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state image sensor in which a plurality of photoelectric conversion element groups are provided on a semiconductor substrate.

With the rapid development of semiconductor and integrated circuit technology in recent years, the development of solid-state image sensors has been strongly promoted. In solid-state imaging devices, pixels are scanned electronically, and the pixel arrangement is determined with high precision using photolithographic technology, so it has the advantage that image distortion is less likely to occur when imaging a subject, and the imaging tube It is expected that it will be commercialized as an alternative. If the application is limited to public funds for use as a television camera for home VTRs, solid-state image pickup devices that provide sufficient reproduced images with a sufficient number of pixels are being put into practical use. However, if we assume a television camera for a station or a television camera as an information processing terminal, no element with sufficient performance has been developed.

FIG. 1 is a schematic diagram illustrating the structure of a conventional solid-state image sensor, which is called an interline solid-state image sensor. In the figure, for convenience of explanation, an element having (3×3) pixels is shown. In the figure, 1 is a photoelectric conversion element, 2 is a vertical register, 3 is a horizontal register, 4 is an output circuit, and 5 is an output terminal. Since the interline solid-state image element is widely known, details of its operation will be omitted.
Write only an overview. - Signal charges photoelectrically converted in a vertical scanning period (field or frame) are moved in parallel to corresponding positions of the vertical register 2 within a vertical blanking period. In FIG. 1, the transfer gate electrode installed between the photoelectric conversion element 1 and the vertical register 2 to control the movement, and the channel stopper to achieve the desired movement are omitted. . The signal charges that have been moved in parallel to the vertical register 2 are sequentially moved downward every -horizontal scanning period. On the other hand, the horizontal register 3 receives and removes signal charges from the vertical register 2 during the horizontal blanking period, and sequentially moves them to the left in FIG. The signal charges reaching the output circuit 4 due to this movement are sequentially converted into voltage signals, and a time-series image signal is outputted via the output terminal 5. Registers 2 and 3 in FIG. 1 are analog shift registers composed of charge-coupled devices or bucket brigade devices. According to this operation, the photoelectric conversion element 1, from which all the signal charges have been read out over a -vertical scanning period, accumulates an amount of charge corresponding to the amount of incident light. −
At the end of the vertical cycle, the signal charges are transferred from the photoelectric conversion element 1 to the vertical register 2 again. In this interline type element, since the photoelectric conversion element group and the register group are spatially multiplexed, the area of the chip surface is reduced, and an improvement in yield and a reduction in price can be expected. However, it is known that in solid-state imaging devices, as the operating temperature increases, the dark current increases and the output voltage when there is no incident light increases. If the device is made of silicon, a 10° C. temperature increase will approximately double the dark current. Considering that normal silicon integrated circuits are guaranteed to operate within a temperature range of 0° C. to 70° C., the device is also required to operate normally within this temperature range. However, if we use the above-mentioned relationship, the dark current line at 70°C is about 100 times higher than the dark current at θ°C, so unless the dark current is automatically corrected by electrical signal processing, the mosquito element It is difficult to expect that it will be put into practical use. To make it easier to correct such dark current, it is preferable to provide an optical black in the element. The optical black can be obtained by shielding one or more rows of photoelectric conversion elements vertically arranged in the element with an opaque film. In the example of FIG. 1, the first photoelectric conversion element group 7 constituting the row on the right side,
8.9 is exemplified as optical black.

In addition, unless an opaque film for light shielding is placed on the vertical register group as exemplified in 2, the signal charges generated by the incident light during the period when the signal charges are moving in the vertical direction (that is, the vertical scanning period) It is known that since charges are added to the signal charges, a white line called smear appears in the reproduced image, severely degrading the image quality. For this reason, an opaque film must be arranged over the registers. Usually, the opaque film is composed of a metal electrode such as aluminum. FIG. 2 shows a structural cross-sectional view of the section AA' shown in FIG. Note that this figure merely shows a conceptual cross-sectional view of the structure for convenience of explanation, and does not necessarily correspond to the actual element in terms of dimensions. In the figure, 10 is a semiconductor substrate of a first conductivity type (e.g., p-type), 11 is a diffusion layer of a second conductivity type (e.g., n-type), which forms a p-n junction with the substrate 10, It constitutes a photoelectric conversion cable l. 12 is one transfer electrode constituting the vertical register 2, 13 is the aforementioned transfer gate electrode, 14 and 1
4/ is the opaque film, and 15 is a channel stopper.

The transfer electrode 12 and the gate electrode 13 are arranged on the substrate 10 via an insulating film (not shown), and the opaque film 1
4.degree. 14' is also arranged with the electrodes 12 and 13 through an insulating film. The channel stopper 15 is provided in order to move the signal charges accumulated in the diffusion layer 11 in one direction under the transfer electrode 12 via the gate electrode 13. Acts as a potential barrier. Moreover, 16 is an opaque film for light shielding provided on the upper part of 8. The shell film 16 can be configured to be the same as 14, or only the area corresponding to 16 of the resin layer (not shown) provided on the surface of the structure shown in FIG. It is also possible to reduce the rate.

According to the operation of the element as described above, at the end of the -horizontal scanning period, a signal is obtained from 7,8°9 on which 16 was deposited. The signal contains only the dark current component mentioned above and does not include the charge generated by the incident light.
The level of this signal is regarded as a true black level, that is, a black reference signal, and when the signal obtained from 5 is amplified by AC, the black signal level can be reproduced by DC using a clamp circuit. According to the signal processing, even if the operating temperature of the element increases, fluctuations in the signal level due to dark current can be prevented, and a stable image signal can be automatically obtained. In the above explanation, the case where optical black is applied only to the right column of the element is illustrated, but in general, multiple adjacent columns are optically black, or the optical black area is applied to the left side of the element. There will be things like setting things up. In such a conventional example, it is known that a substantially true black level can be obtained by the optical black structure. However, when the amount of incident light becomes extremely large or when the incident light contains a large amount of near-infrared light, there is a drawback that the assumed true black level fluctuates toward the white level. One of the causes of such fluctuations is that charges generated deep in the substrate 10 due to near-infrared light are diffused into 16
It is accumulated in the photoelectric conversion element directly below. Such fluctuations have adverse effects such as horizontal stripes appearing in the captured image and the entire screen becoming whitish due to a raised black level, resulting in extreme deterioration of image quality. Especially in solid-state image sensors used for professional use, 1. Such variations in black level narrow the field of application.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such conventional drawbacks and provide a solid-state image sensor that stabilizes the black level.

According to the present invention, a plurality of photoelectric conversion element groups formed on a semiconductor substrate having one conductivity type, a vertical resistor group having a buried channel structure in multiple rows, and a vertical resistor group provided adjacent to one end of the vertical resistor group a horizontal register, an output circuit provided at one end of the horizontal register, a means for periodically moving signal charges from the photoelectric conversion element group to the vertical register, and a means for periodically transferring signal charges from the photoelectric conversion element group to the vertical register; In an interline solid-state image sensor having a light shielding means provided on the upper part of the photoelectric conversion element group, the first photoelectric conversion element group and the first vertical light shielding means provided adjacent to the element group. The substrate formed under the resistor group includes a first buried layer of an opposite conductivity type, a second photoelectric conversion element group that does not include the second photoelectric conversion element group, and the second element. a second buried layer of a conductivity type opposite to that of the substrate formed below the second vertical resistor group provided adjacent to the vertical register group; A solid-state imaging device is obtained, characterized in that a light shielding means is provided above an intermediate region between the buried layer and the buried layer.

Next, the present invention will be described in detail with reference to examples.

FIG. 3 is a sectional view of one embodiment of the present invention. The same figure is the second
The same numbers as those in Figure 1g2 indicate the same components. In this embodiment, both the vertical register and the horizontal register employ a buried channel structure. In the figure, reference numeral 40 denotes a diffusion layer constituting 8, which is one of the first photoelectric conversion element groups, and 50.5
1 is a buried layer of conductivity type opposite to that of 1°, and 8 is one of the adjacent photoelectric conversion element groups, and one of the first vertical resistor groups provided in contact with the element. 50, which is a first buried layer provided in the substrate lo at the lower part of a certain mutually spaced area, and one of the second photoelectric conversion element groups that does not include the photoelectric conversion element group No. 0, for example, 11. , a second vertical resistor group 53 provided adjacent to the device, and a second buried layer 51 provided in the substrate 10 below. In this example, since a buried channel structure is adopted, the angle of 11°4
0 is selected to be the opposite conductivity type to 50.51, ie, the same conductivity type as 10, and 15 is selected to be the same conductivity type as 51, ie, the opposite conductivity type to 10. 42 is a high concentration region having the same conductivity type as 10; It will be shown next that if such a configuration is adopted, the factors that induce variations in the black level in the conventional example described above can be effectively and easily removed. The depth of the junction is set in advance so that the incident light including near-infrared light is absorbed inside the buried layer 51 and the depletion layer of the pn junction formed by 51 and 10 and converted into electric charge. . Since the relationship between such element structure and absorption of incident light is well known, a detailed description of the design method will be omitted. Note that in actual applications of the device, near-infrared light with a wavelength of 1 μm or more is unnecessary, so it is often excluded by an infrared cutoff optical filter provided on the top of the device. For this reason, charges are not generated in the 10 regions that are not depleted. On the other hand, at the ends of 51 and 50, an electric field as exemplified by 54.55 acts, so the charges generated in the area of 51 reach the area of 50 and are accumulated in 40 or leak into the % scale. There's nothing wrong with that. From this explanation, it was understood that according to this embodiment, fluctuations in the black level can be prevented when strong incident light is present. Note that in this embodiment, 42 is wider than 15, so
It is necessary to increase the number of constituent elements of the horizontal register 3 corresponding to the portion facing 42. Such an increase in the number of constituent elements will increase power consumption in the driver that drives the register, but since the rate of increase in the number of elements is less than a few percent, this cannot be a significant problem. Further, 42 is provided in the intermediate region of 50.51, so that an electric field of 54.55 is realized, that is, 50.
゜51 acts to be electrically isolated within the cross section, the end of 42 may be in contact with 50.51, and the width of 420 shall be selected as appropriate in the design. do. Further, if 50 and 51 are electrically isolated within the cross section, 42 is not necessarily necessary, and the process steps can be simplified by omitting it.

Opaque film 14 provided on top of 42 in substrate 10
This is necessary to prevent charges generated by the incident light in the region 2 from being drawn into the area 50 by the electric field 55. However, although the opaque film provided on the upper part of 42 is shown in FIG. 3 in which 14 is extended, the present invention is not limited to this, and 16 is extended in the left direction in the figure. Any configuration method may be used.

The present invention has been described above in detail using examples. In this specification, for convenience of explanation, the case where the optical black is on the right side of the element is illustrated, but it may be on the left side or on both sides, and furthermore, there may be multiple adjacent columns. Also good. Note that the means for realizing the light-shielding film in 16 is not limited to the same or similar process as in 14.14', for example, the method using a metal vapor deposition film such as aluminum, but also the method by which the light-shielding film is brought into close contact with or in close proximity to the surface of the element. The present invention also includes realization by reducing the transmittance of the resin or glass provided. Further, the present invention is not limited to an interline type solid-state image sensor, but can be widely applied to other solid-state image sensors, such as a frame transfer type solid-state image sensor.

[Brief explanation of the drawing]

FIG. 1 is a conceptual structural plan view of an interline solid-state image sensor, FIG. 2 is a cross-sectional view taken along line AA', and FIG. 3 is a conceptual structural cross-sectional view showing an embodiment of the present invention. . 1...Photoelectric conversion element, 2...Vertical register, 3...Horizontal register, 4...Output circuit, 5...Output terminal , 10...substrate, 11...diffusion layer, 12...transfer electrode of vertical register, 13...transfer gate electrode,
14.14', 16... Opaque film, 7,8°9... Light-shielded photoelectric conversion element, 40...
・Diffusion layer, 42...High concentration region, Akira 2,53・
...Vertical register area, 50.51...
Buried layer, 54.55...mountain/electric field.

Claims (1)

[Claims] A plurality of photoelectric conversion element groups formed on a semiconductor substrate having one conductivity type, a vertical register group having a buried channel structure in multiple rows, and a horizontal register provided adjacent to one end of the vertical register group; an output circuit provided at one end of the horizontal register; a means for periodically transferring signal charges from the group of photoelectric conversion elements to the vertical register; and a first photoelectric converter located at an end of the group of photoelectric conversion elements. In an interline solid-state image sensor having a light shielding means provided above a conversion element group, the first photoelectric conversion element group and the first vertical register group provided adjacent to the element group a first buried layer formed at the bottom and having a conductivity type opposite to that of the substrate; a second group of photoelectric conversion elements that does not include the first group of photoelectric conversion elements; and a second group of photoelectric conversion elements that is adjacent to the second group of elements; A second buried layer having a conductivity type opposite to that of the substrate formed below the second vertical resistor group provided is disposed separately from each other, and the first and second buried layers are separated from each other. A solid-state image sensor characterized in that a light shielding means is provided above an intermediate region.